Need help about school project

Me and my friend are trying to make an autonomous drone without GPS that can go inside the school, but we are not sure which flight controller or which software we should use. Among our preferences is to use a raspberry pi with a pixhawk, but I saw a radiolink mini pixhawk on the internet for half the price of a fake pixhawk, what should I do? (maximum budget is $200) or is there an easier and cheaper system than this one? If so, what are they?

There’s a list of compatible hardware at Autopilot Hardware Options — Copter documentation.

Radiolink and “fake” Pixhawks are generally not recommended due to compatibility issues with ArduPilot.

For your case, one of the Kakute or Matek multicopter boards would work well.

What sensors are you planning to use for indoor navigation?